1. Field of Application
The present invention relates to a method for forming a shaped article from a defect-free oxide superconducting material, more particularly, it relates to a process for producing a magnetic shielding container which utilizes Meissner effect.
2. Prior Art
Conventional processes for producing bulk materials from an oxide superconductor comprise, in general, packing a powder material and then sintering the resulting powder compact. It is also well known to conduct the sintering step by HIPping (Hot Isostatic Pressing) and the like to obtain a further densified material, or by melting a part of the composition (sometimes referred to as a "partial melting process") to increase the density of the bulk material.
As an improved process for powder sintering, there is known a process in which a paste, etc., obtained by dissolving the powder of an oxide superconductor to a pertinent dispersion medium, is utilized. The paste or slurry thus obtained may be directly shaped into a sheet by a doctor blade process and the like and sintered; otherwise, it may be applied to a base of a desired shape and sintered to obtain freely an oxide superconductor material of a desired shape.
Furthermore, study on a process involving chemical vapor deposition (CVD) and the like for coating a pertinent substrate or base with a thin film or a thick film of oxide superconductors is also in progress, particularly, for use in wire materials.
Although extensive studies are in progress, conventional processes for producing oxide superconducting materials are still far from being practical. The powder sintering process, for instance, allows almost no selection of shape and size; moreover, it accompanies technological difficulties in producing large scale sinterings, even if a material other than a superconducting material were to be sintered. Accordingly, it is next to impossible to sinter a large-scale superconducting material using this process. A HIPping process is advantageous in that it provides dense sinterings having high density, however, this process again, cannot be applied to the production of a large scale bulk material.
The process using a paste material and the like is superior in producing superconducting materials at a desired shape, and is now being applied to practical processes for manufacturing superconducting magnetic shields which are to be trial marketed. The superconducting materials produced by this process, however, result inevitably in porous sinterings because the organic matter and the like having incorporated in the dispersion medium escape during the sintering process. Thus, such superconducting materials often suffer insufficient quality for use as a magnetic shield.
The coating process using CVD and the like provides superconducting materials of best quality. However, the film which is obtained by the process is too thin to be used as a magnetic shield, because a certain volume as a bulk, i.e., a container having a wall with certain thickness, is necessary to yield a sufficient magnetic shielding effect. Thus, concerning the film deposition rate and other factors, the CVD process and the like at present cannot be applied to such products as magnetic shields.